Isotopic constraints on global marine iron cycling, ocean productivity and deoxygenation

溶解铁是限制海洋初级生产力的关键微量元素。全球海洋铁收支的主要来源通量是大气沉降、沉积释放和热液输入。它们决定了海洋中铁的含量，但仍然缺乏约束。海洋中新出现的铁同位素数据集提供了对关键铁来源的额外限制，因为它们的来源端元特征信息是已知的。在这个项目中，我们将在我们的全球海洋生物地球化学模型中实施铁同位素示踪剂，以提供对这些来源铁通量的额外定量约束。特别是，我们将开发海洋-沉积铁交换的新模块，这是目前海洋铁预算中最大的不确定性。这一新的沉积铁通量分量将明确地解释有机质驱动的还原性通量和非还原性海底溶解通量。根据一个全球观测数据集，还原通量将对底水氧浓度敏感，该数据集表明，随着氧的减少，沉积还原铁通量增强。我们的全球海洋生物地球化学模型将估算不断增加的大气铁污染和变暖引起的脱氧在多大程度上增强了海洋表面的铁通量，从而促进了额外的初级生产力，造成了放大反馈，推动了额外的脱氧。我们假设这种增强的源铁通量-脱氧放大反馈是导致为政府间气候变化专门委员会提供预测的全球地球系统气候模型显著低估当前海洋脱氧速率的关键缺失特征。

Dissolved iron is a key micronutrient limiting ocean primary productivity. The major source fluxes in the global oceanic iron budget are atmospheric deposition, sedimentary release, and hydrothermal input. They determine the amount of iron in the ocean but are nonetheless poorly constrained. A new emerging dataset of iron isotopes in the ocean provides additional constraints on the key iron sources since information on their source end-member signatures is known. In this project, we will implement iron isotope tracers in our global ocean biogeochemical model to provide an additional quantitative constraint on these source iron fluxes. In particular, we will develop a new module for ocean-sedimentary iron exchange, which currently represents the largest uncertainty in the marine iron budget. This new sedimentary iron flux component will explicitly account for both the organic matter driven reductive flux and the non-reductive seafloor dissolution flux. The reductive flux will be sensitive to bottom water oxygen concentrations according to a global observational dataset indicating enhanced sedimentary reductive iron fluxes as oxygen decreases. Our global ocean biogeochemical model will estimate how much the combination of increasing atmospheric iron pollution and warming-induced deoxygenation enhance iron fluxes to the surface ocean that fuels additional primary productivity, causing an amplifying feedback that drives additional deoxygenation. We hypothesize this enhanced source iron flux-deoxygenation amplifying feedback is a key missing feature causing global Earth System Climate models that provide projections for the Intergovernmental Panel on Climate Change to significantly underestimate the current rate of ocean deoxygenation.